tetrapod

any vertebrate having four limbs or, as in the snake and whale, having had four-limbed ancestors.

2.

an object, as a caltrop, having four projections radiating from one central node, with each forming an angle of 120° with any other, so that no matter how the object is placed on a relatively flat surface, three of the projections will form a supporting tripod and the fourth will point directly upward.

tetrapod

/ˈtɛtrəˌpɒd/

noun

1.

any vertebrate that has four limbs

2.

Also called caltrop. a device consisting of four arms radiating from a central point, each at about 109° to the others, so that regardless of its position on a surface, three arms form a supporting tripod and the fourth is vertical

3.

(engineering) a very large cast concrete structure of a similar shape piled in large numbers round breakwaters and sea defence systems to dissipate the energy of the waves

Any of various mostly terrestrial vertebrates that breathe air with lungs. Most tetrapods have two pairs of limbs, though some, such as whales and snakes, have lost one or both pairs. Tetrapods include the amphibians, reptiles, birds, mammals, and various extinct groups, and evolved from lobe-finned fish during the late Devonian Period. Tetrapods are classified according to the structure of their skull into anapsids, diapsids, and synapsids.